The present invention relates to a circuit breaker draw-withdraw apparatus for use with a circuit breaker to move the circuit breaker so as to be connected to or be disconnected from a plug-in base.
Conventionally, a plug-in base for a circuit breaker is mounted on a panel board or other base structure and is wired to circuitry on the base structure. A circuit breaker is installed in the plug-in base by inserting stabs protruding from the circuit breaker into jaws fixed to the plug-in base. The jaw/stab connection provides the primary electrical connection between the circuit breaker and the plug-in base. This connection may also mechanically retain the circuit breaker in the plug-in base.
Withdraw mechanisms have been developed for mechanically drawing a circuit breaker unit into a plug-in base and withdrawing the circuit breaker unit from the plug-in base. An example of such a withdraw mechanism is disclosed in U.S. Pat. No. 5,837,949 to Green et al. The withdraw mechanism described in Green et al. is operated by rotating a screw linkage using a drive tool inserted into the front of the withdraw mechanism which draws the circuit breaker into or withdraws the circuit breaker from the plug-in base. This type of mechanism is advantageous since a high amperage circuit breaker is heavy and thus difficult for a technician to position properly in the plug-in base by hand. In addition, the jaws in a high amp plug-in base may require a high insertion force, making it difficult or impossible for a technician to apply sufficient force to fully insert the stabs into the jaws.
A circuit breaker withdraw mechanism typically includes a component attached to the plug-in base and a component attached to the circuit breaker. Installation of the withdraw mechanism may take place in the field, in a supplier warehouse or at the circuit breaker production plant.
It is desirable to ensure that the screw linkage of the withdraw mechanism ceases operation after the drive tool rotates the screw linkage past its operational range of motion, both in the withdraw and install directions. In lower amperage applications, this may be accomplished by providing stops at either end of the screw linkage travel, preventing rotation of the screw linkage past the operational range of motion. However, in high-amperage applications stops are not adequate since greater torque must be applied to the drive tool and the mechanism may be damaged by over-travel. Accordingly, there is a need to provide improved over-travel protection in a withdraw mechanism.